JPS61269573A - Halftone signal processing circuit in television receiver - Google Patents

Abstract

PURPOSE:To make characters easy to see by giving a half tone signal to an automatic brightness limiting circuit during a blacking pulse output period of a character signal to output the result to a video signal processing circuit as a beam current limit signal thereby decreasing the brightness around the character. CONSTITUTION:A halftone signal S1 given to the 1st input section 13 is given to a base of a transistor (TR) 15 of a circuit means 12 and a blanking pulse S2 during a character signal blanking period in the high level given to the 2nd input section 14 is given to a base of a TR 16. A halftone signal S3 represented to a collector of the TR 15 is a waveform where the level corresponding to the surrounding part of a character signal to the subjected to halftone goes to actually a high level and a low voltage equal to a charging voltage of a capacitor C18 is given to a beam current limiting circuit 11 of the automatic brightness limiting circuit 6 when the signal S3 is at a high level and a high voltage nearly equal to a power supply voltage VCC is given when at a low level. Thus, the brightness around the characters is decreased to make easy to see.

Description

Detailed Description of the Invention (Technical Field) The present invention relates to a halftone signal that is provided in a television receiver and processes a halftone signal to reduce the brightness around characters on the screen (to create a halftone). Regarding processing circuits.

(Prior art) When displaying character signals from teletext broadcasts or personal computers on the screen of a television receiver, if the brightness around the characters on the screen is high, the characters become very difficult to see, so it is necessary to make the characters easier to see. To achieve this, it is necessary to lower the brightness around the characters.

One means for this purpose is a circuit that lowers the level of the video signal portion of the video signal excluding the vertical and horizontal synchronization signals and the portion that overlaps with the halftone signal, but the circuit configuration is The drawback was that it was complicated.

(Objective of the Invention) An object of the present invention is to reduce the brightness around a character to make it easier to see the character using a simple circuit configuration.

(Structure of the Invention) The present invention firstly outputs a beam current limiting signal for limiting the beam current of the picture tube to a specified value or less to a video signal processing circuit in accordance with a detected value of a change in the picture tube anode current. It uses an automatic brightness limiting circuit that automatically limits brightness. Second, by providing a circuit means for supplying a halftone signal for lowering the brightness around the characters on the screen to the automatic brightness limiting circuit during the blanking pulse output period of the character signal, the automatic brightness limiting circuit can be controlled by the circuit means. A halftone signal from the beam current limit signal is outputted to the video signal processing circuit as the beam current limit signal.

(Example) FIG. 1 is a circuit diagram according to an embodiment of the present invention.

The television receiver of this embodiment includes a video signal processing circuit 1 that processes video signals, and an amplifier that amplifies R, G, and B signals from the video signal processing circuit 1 and outputs the amplified signals to the cathode of a picture tube 2. 3, 4.5. Also,
This television receiver has an automatic brightness limiting circuit 6 for preventing excessive current from flowing through the picture tube 2 due to abnormally high brightness.

This automatic brightness limiting circuit 6 is well-known (for example, rNHK Color TV Receiving Technology, August 1, 1999).
Japan Broadcasting Corporation), flyback transformer 7
The negative voltage generated when the picture tube anode current flowing through the secondary high-voltage winding 8 charges the capacitor 9 and the resistance 1
0, the beam current limiting circuit 11 outputs a beam current limiting signal to the video signal processing circuit 1 to limit the beam current of the picture tube 2 to below a specified value. This automatically limits the brightness.

In this embodiment, the automatic brightness limiting circuit 6 provided in such a normal television receiver is used to reduce the brightness around the characters by the following circuit means 12.

Reference numeral 12 designates one stage of circuitry 3 for applying a halftone signal for lowering the brightness around characters on the screen to the automatic brightness limiting circuit 6 during the character signal blanking pulse output period. This circuit means 12 receives a high-level noftone signal St as shown in FIG. 2(a) and a high-level signal St as shown in FIG. A second human power unit 14 is provided with a blanking pulse S2 serving as a signal blanking period.
The halftone signal St applied to the human power section 13 is applied to the base of the first transistor 15. The character signal blanking p<)res S2 is applied to the base of the second transistor 16. The base of the first transistor 15 is grounded via the collector of the second transistor 16 and the emitter. Therefore, the halftone signal Sl applied to the first input unit 13 is input to the collector of the first transistor 15 in coincidence with the 71 level period of character signal blanking l<res S2 applied to the second human input unit 14. Figure 2 (C)
The 1-foottone signal S3 corresponds to the periphery of the character signal that is actually to be halftone. The waveform has a waveform in which the level changes from 7 to 1.

The third transistor 17 is turned off when the first transistor 15 is turned off (
or on), that is, when the halftone signal S3 is at a high level (or low level). A capacitor 18 is connected to the emitter of the third transistor 17. This capacitor 1
8 is charged with a voltage obtained by dividing the power supply voltage Vcc by a resistor 19 and a variable resistor 20. This variable resistor 20 is for adjusting the halftone level.

When the halftone signal S3 is at a high level for the periphery of characters, the third transistor 17 is on, and when the third transistor 17 is on, a diode is connected to the beam current limiting circuit 11 of the automatic brightness limiting circuit 6. A low voltage approximately equal to the charging voltage of capacitor 18 is applied via 21 . Further, when the noft tone signal S3 is at a low level, the third transistor 17 is turned off, and a high voltage approximately equal to the power supply voltage Vcc is applied to the beam current limiting circuit 11.

The beam current limiting circuit 11 generates a beam current such that when a low voltage is applied from the diode 21, the level of the video signal is halved, and when a high voltage is applied, the level of the video signal is increased to the brightness of the character signal. A limiting signal is given to the video signal processing circuit 1.

Therefore, the automatic brightness limiting circuit 6 outputs the beam current limiting signal to the video signal processing circuit 1 in accordance with the output from the circuit means 12.
The video signal processing circuit 1 processes the video signal so as to reduce the brightness around the characters using the beam current limiting signal, and outputs the processed video signal to the picture tube 2 via the amplifiers 3, 4.5.

The shaded area in FIG. 3(a) shows the position of the picture tube 2 on the screen corresponding to the halftone signal Sl, and FIG. 3(b) shows the position of the picture tube 2 on the screen corresponding to the character signal (T V Y M). Figure 3 (C) shows the position of the halftone signal S on the screen.
3 shows the position of the picture tube 2 on the screen corresponding to 3.

(Effects of the Invention) As described in item 2 below, according to the present invention, a circuit provides a halftone signal for reducing the brightness around characters on the screen to the automatic brightness limiting circuit during the blanking pulse output period of the character signal. The automatic brightness limiting circuit provided in the television receiver outputs the halftone signal from the circuit means as the beam current limiting signal to the video signal processing circuit, so that the brightness around the characters can be reduced. As a halftone signal processing circuit for lowering the brightness, a normal automatic brightness limiting circuit is used as is, and the circuit means only needs to output the halftone signal to the automatic brightness limiting circuit during the blanking pulse output period. The circuit configuration becomes extremely simple.

[Brief explanation of the drawing]

FIG. 1 is a circuit diagram of an embodiment of the present invention, and FIG. 2 is a time chart of each signal during one horizontal scanning period. FIG. 3 is a diagram for explaining the display of characters on the screen. 1 is a video signal processing circuit, 2 is a picture tube, 6 is an automatic brightness limiting circuit, 2 is a beam current limiting circuit, 12 is a circuit means, 13
．． 14 is an input section, Sl, S3 is a halftone signal, S2
is a blanking pulse, and S3 and S4 are video signals.

Claims (1)

[Claims] (1) Automatically limit the brightness by outputting a beam current limiting signal that limits the beam current of the picture tube to a specified value or less to the video signal processing circuit according to the detected value of the change in the picture tube anode current. an automatic brightness limiting circuit; and circuit means for applying a halftone signal for reducing brightness around characters on the screen to the automatic brightness limiting circuit during a blanking pulse output period of the character signal, the automatic brightness limiting circuit comprising: A halftone signal processing circuit for a television receiver, characterized in that the halftone signal from the circuit means is output to the video signal processing circuit as the beam current limiting signal.